Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$99.27	10.175%	$109.3707	$109.37	$109.35	$109.40
Purchase #2	$116.43	5.129%	$122.4017	$122.40	$122.40	$122.40
Purchase #3	$229.50	11.272%	$255.3692	$255.37	$255.35	$255.40
Purchase #4	$47.59	10.280%	$52.4823	$52.48	$52.50	$52.50
Purchase #5	$204.81	5.377%	$215.8226	$215.82	$215.80	$215.80
Purchase #6	$118.43	3.817%	$122.9505	$122.95	$122.95	$123.00
Purchase #7	$208.46	5.762%	$220.4715	$220.47	$220.45	$220.50
7 purchase totals =	$1,024.49		$1,098.8685	$1,098.86	$1,098.80	$1,099.00